Oh fish! killer threatens Bengal's favourite dish

West Bengal's eternal favourite, hilsa, and prawn may be at risk. An "invisible" and primitive fish-killer that has played havoc with the fishing industry across the globe, inflicting losses worth billions of dollars in several countries, is now knocking on the doors of the state.

A team of city-based marine scientists leading a study on marine life, in June stumbled upon a species of highly toxic microscopic alga, Cochlodinium, in the creeks of Sunderbans and coastal waters of Shankarpur.

The species, the experts said, could wreak havoc on popular varieties of fish breeding in the coastal waters and spell doom for the marine fishing industry in the state. West Bengal currently accounts for two lakh tonnes of marine fish every year.

"We have already shot off a letter to the Union ministry of earth sciences to alert them about the find," said Punyasloke Bhadury, assistant professor of biological sciences at the Indian Institute of Science Education and Research, who is heading the study.

The same team had earlier discovered some new colonies of phytoplankton (microscopic plants), Pseudonitzshia, which had been found to be releasing deadly neurotoxins in the estuaries of the Sunderbans.

Alarmed with the findings, the ministry of earth sciences had released funds to conduct a detailed study on such harmful colonies of plants and animals along the Bengal coast. The fresh revelation is a result of the study commissioned by the ministry.

"Cochlodinium is nearly 10 times deadlier than Pseudonitzshia," Bhadury said. While Pseudonitzshia is a much more evolved form of microscopic plants, the origin ofCochlodinium can be traced back to the origin of life on the planet."

However, the scientists have yet to crack how the deadly algae prey on the marine life. While some say they release toxins in the water, killing microscopic plants, animals that the fish feed on, others contend that the fish die on contact with the algae's toxin.

The species was first reported from the Caribbean Sea along the southern coast of Puerto Rico in the early 1960s. Cochlodinium blooms were previously rare, but have emerged across the globe during the past decade. The species has since been found to inhabit the coastal waters of Indonesia, Malaysia, and Arabian Gulf.

The blooms are mostly known to inhabit the coasts of Japan and South Korea and have caused more than $100 million in annual losses to fisheries from fish kills."However, this is the first time these have been reported from any mangrove areas in Asian countries," Bhadury said.

Quizzed about what led the species to inhabit the Bengal coast, the experts said the source could likely have been the ballast tanks of ships sailing on the coastal waters. Many cargo ships carry water to fuel ballast tanks. The water in huge vessels is lugged on board every time a ship anchors at a particular port and dumped at or near another port. Ballast waters, said sources, have been the carriers of many such species.

What is alarming is that the water in the Sunderbans differs from those in Japan and Korea in terms of temperature and salinity, leading many to contend that the species could well have adapted to the new eco-system.